Radiation Belt Electron Precipitation: Recent BARREL Observations and Future Missions

Resonant wave-particle interactions with plasma waves (e.g. plasmaspheric hiss, whistler mode chorus, and electromagnetic ion cyclotron (EMIC) waves) are often cited as one of the main loss processes that drive the variability of electron fluxes in the Earth's radiation belts . The evolution of our understanding of the radiation belt electron precipitation, the driving mechanism for such events, and its relative impact on radiation belt particle fluxes has moved from single point measurements to the dawn of simultaneous multi-point measurements and conjunction studies. The BARREL mission, as a mission of opportunity to the Van Allen Probes mission, deployed an array of balloon borne detectors to observe radiation belt electron losses into the atmosphere. This mission offered extended periods of time in conjunction with Van Allen Probes and polar LEO orbiting satellites. Conjunction studies have been used to correlate observed plasma waves on Van Allen Probes with electron precipitation observed on BARREL and further constrained the spatial scale of electron precipitation [1-3]. These studies, in combination with theoretical modeling, have shown that the parameter space involved in wave-particle interaction extends beyond our measurements. Therefore, in order to further advance our understanding of these phenomena and their impact on the radiation belts we need to broaden the scope of our measurements and narrow the assumptions and undefined parameters that go into the theory.